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Topic Review (Newest First)

09-30-2013 04:26 PM

sloop.odyssey

Re: Boy killed by lightning in our anchorage, what would you do?

Lightning scares the hell out of me, but if I stayed ashore every time "scattered thunderstorms" are predicted around Cape Cod in the summer, I'd never sail. I have never been struck, so can't guarantee this works, but fastening one end of heavy-duty jumper cables to the inboard backing plate of my sloop's chain plates, and the other end to the keel bolts, would seem to provide a good temporary solution. (I've also grounded the mast to a keel bolt.)

01-15-2013 05:32 PM

peterconway

Re: Boy killed by lightning in our anchorage, what would you do?

Lightning kills as it passes thru critical tissue, ie the heart and vital organs, fortunately because of its high frequency it is more likely to flash over the body, verses entering and exiting. Many time it's victims are burned at the skin level, their clothes shredded off and they survive.
Any electricity, even small amount can kill if it passes through and disrupts normal heart rhythm. Other tissue is cooked to the point of failure.
The best defense is to avoid, but if you can't avoid, there are things you can do to increase you chances of survival. The MOST beneficial thing would be to crouch, with you ankles touching and not hold with a hand hold. This makes you the lowest possible target, and by keeping you ankles together will allow the difference of potential to be confined to the feet and not travel through the legs. The current, if it is radiating will travel up a foot, cross at the contact point of the ankles, an exit the other foot. Remember, electricity is stupid....it's only goal is to get to ground, the best and easiest way it can.

11-15-2012 05:38 PM

hellosailor

Re: Boy killed by lightning in our anchorage, what would you do?

If you've ever read the publicly available papers on what "military grade hardened" electronics and systems are, you would understand why no one can afford to put them on a boat. Check out what is needed to "EM harden" a building, you'd have to build a submarine to do it to your boat.

Similarly, why not ground the rudder? Uh, because it is already "grounded" by being fully submerged in the water. Unless you want to run a cable down to an earth anchor grounding rod, that job is already done.

Lightning protection works frequently but never completely. Check out PolyPhaser and install one in your antenna line to protect your VHF. But it won't protect your antenna, antennas are sacrificial parts. If you want to protect the antenna, you submerge the boat before the storm. Honest, that's how it is done.

11-15-2012 02:29 PM

steel

Re: Boy killed by lightning in our anchorage, what would you do?

Has anyone had the VHF antenna hit while having a properly installed lightning arrestor on the VHF antenna feed line? The ground of the lightning arrestor has to be connected to the mast ground with its own wire.

Of course if the EM field created is so strong that it destroys electronics which aren't plugged in then there isn't much you can do except get military grade hardened electronics.

And why not ground the rudder? You want to have 20,000v between your wheel and the throttle control which is hooked to the engine which could be hooked to the different mast ground?

11-13-2012 02:38 PM

Flatballer

Since I have some experience here I'll throw my two cents in. I was on a boat struck by lightning. Cruiser, connected to shore power, well grounded boat. Standing in companionway watching storm. There hadn't been lightning. Next thing I knew I was laying on the cabin sole. Not sure if I jumped or fell. Someone across the ICW in a house thought I was dead because I just stayed down below, they sent the Marina person down, thinking they were gonna find a body. It vaporized the VHF antenna on the mast, the SSB and VHF died, the little lightning thing on the mast was gone. Everything else was fine. Witnesses say it was a direct strike on the mast. All I know is it was the loudest thing I've ever heard. I'll take a well grounded boat any day over being anywhere else. Even though it's the tallest thing around and presents a good path to ground, it's a great place to be.

I'm an EE and I'll tell you we still know very little about lightning. We still can't even figure out which direction it goes or what really causes it, much less how to prevent it.

Shame about the death. I'd recommend staying in the boat and on the water.

Sent from my DROID RAZR using Tapatalk 2

11-09-2012 06:10 PM

OPossumTX

Re: Boy killed by lightning in our anchorage, what would you do?

Normal fuses provide no effective lightning protection. The little wire in the fuse vaporizes instantly and coats the inside of the glass with a thin layer of conductive metal.

Now if the potential from the strike is high enough, the now metal metal film resistor which used to be a fuse will explode from the pressure inside and when you open your little plastic fuse holder, you will find what looks like grey sand in there between the two little cups that were the ends of the fuse. Needless to say, what ever that fuse was supposed to protect is probably smoked too.

11-02-2012 10:37 PM

fallard

Re: Boy killed by lightning in our anchorage, what would you do?

hellosailor has a point about not needing a perfect faraday cage to get some protection, with a car providing another example. That said, the whole boat as an approximation to a faraday cage only applies if the boat is all metal. The overwhelming majority of recreational sailboats are plastic.

It is more likely that the typical sailor can only get the benefit of a faraday cage that is much smaller, like an oven or an aluminum foil wrap. It can be inconvenient to disconnect and remove your electronics to an oven, so the aluminum foil trick may be more practical, as long as the wiring is disconnected. I agree that just switching off a breaker does not guarantee protection, as I noted in my previous post. But I also noted my personal experience that completely disconnecting your electronics does not provide protection against the electromagnetic pulse from a lightning strike.

11-02-2012 07:37 PM

hellosailor

Re: Boy killed by lightning in our anchorage, what would you do?

sallard, overall I agree with you but note that you don't need a theoretically perfect faraday cage in order to have an effective one. Aircraft windows are about the same size as boat hatches, yet avionics pros will tell you that the aircraft basically IS a very effective faraday cage and they rarely take damage even when struck by lightning. The skin still conducts most of the charge on the OUTSIDE of the aircraft, the same way that AC power is largely conducted on the outside skin of a wire. I don't know the physics, I just have the Cliff notes.
Similarly, if your electronics were "protected" only by having the brealers thrown, that's no protection. The air gap in a breaker flashes over and fails at around 3000 amps discharge. The lighning is pushing way more current and voltage than a breaker is designed to protect against, you might as well say that a spark plug's air gap can "protect" against an ignition system's coil power. Of course, it doesn't.
While professional broadcasters DO use more effective lightning protecction devices (like PolyPhaser) and those devices work very effectively to protect towers and transmitters that never are unplugged, those folks also do go off the air due to lightning damage at times. Despite the best of protection and expert installation.
Bottom line, to protect electronics you do what radio operators have done for a very long time: You ground the antenna cable, outside of the radio room (i.e. above deck or at the mast) and the antenna and cable iteself are sacrificial items. Once the electronics are really isolated, they are safer. But that means unplugging everything every time you step off the boat, and then the connectors fail, or the job becomes a nuisance that just won't get done.
Lightning: God's way of playing golf. Always hitting par, often scoring hole in one.

11-02-2012 06:32 PM

fallard

Re: Boy killed by lightning in our anchorage, what would you do?

Not being deliberatively argumentative, but steel's point about a steel hull providing a faraday cage would be true if there weren't any holes in the steel larger than the openings in the mesh on your microwave window. Lightning is a very short-duration electrical event with correspondingly high frequency (e.g., radio frequency) components that will pass through your hatches, companionway, etc.

Also, surge protectors can't hurt, but are not likely to make much of a difference in a direct strike, which will not only electrify your wiring with a conducted, transient high voltage, but will also generate a radiated electromagnetic pulse (EMP) that can impress a high voltage across a circuit board--well above the breakdown voltage of any semiconductor.

How do I know that? I lost a wheel pilot control unit in an indirect strike. It was sitting on a shelf, not connected to anything. I lost all of my other electronics, too, including a VHF that had in-line littlefuses that looked like popped flash bulbs. That radio circuit was electrified, even though its circuit breaker and the master breaker were in the "off" position.

I also wouldn't ground your tiller/wheel, unless you don't want your mast to act as your primary lightning rod to keep the main discharge away from the cockpit. There's a reason that injuries from lightning strikes are less severe or less numerous statistically on sailboats compared to power boats. It's all about the height of the mast and the larger cone of protection on a sailboat!

I've already indicated in previous post that I have had 2 lightning events with my current sailboat. Your best defense is an insurance policy that does not depreciate your electronics (as does BoatUS, last time I checked).

What about steel sailboat?? if your inside would they act as a giant faraday cage? and if your on the outside of the boat? would the electricity run through the hole boat or hit the mast, shroud and stays and then use the shortest path to water??

Pierre

A full metal hull should do that. But don't forget about the mast top VHF antenna and the other wires going up there. There needs to be lightning arrestors on the antenna feed line and also on the power wires going to the lights. Else the surge will just come in through there and spread in to the whole electrical system.

As for the wheel and tiller, they should be electrically connected to the ground that the mast uses. This ensures that everything is at the same potential and there isn't a different voltage at your mast, rigging and lifelines than there is on your wheel or tiller.

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